In many areas it has been found to be advantageous to enhance a grey image with color in regions of the total image to display variable phenomena which is without natural color. For example, weather radar images are color enhanced to show cloud density since that is particularly related to storm intensity in thunder storms, and medical images generated by a variety of machines produce color enhanced images to depict such things as blood flow in organs that are imaged by ultrasound. Many other applications exist and would be of interest so that an easily readable, permanent record could be made for later study, such as the air traffic pattern in the vicinity of an airport at just prior to, and at the time of, a sudden, premature total loss of vertical separation between an aircraft and the earth. Such an image could be color enhanced to show the altitudes of the various aircraft in the region showing both horizontal and vertical separation between them.
In the medical arts it has been demonstrated that such color enhanced images improve the diagnostic capabilities from a single image, however, the methods and color media for storing these images leaves a lot to be desired as far as cost, speed at which they can be prepared and the resolution of the image.
Ultrasound images are typical of the medical applications for artificially color enhanced images in use today. The basic ultrasound image is a black and white, or grey scale, image that can be viewed on a monitor in real time or stored on film. To improve the diagnostic value of ultrasound images, many ultrasound machines include a color doppler option for adding, in the form of color enhancement, the location and velocity of blood flow at the instant that the image is recorded. When the color doppler option is in use, the image produced includes black and white regions where the doppler does not detect blood flow with a velocity that is above the minimum selected threshold level, and variable color regions where the doppler system detects blood flow at various velocities. For example, there are generally two velocity scales, one for blood flow toward the transducer and another for blood flow away from the transducer. Thus, red through yellow might be selected for blood flow in one direction and blue through green for blood flow in the other direction. In the final image, the color information is substituted for the black and white information where the flow rate of the blood exceeds the preselected threshold level.
At present, the media available for recording these color images are Polaroid instant color film, color thermal prints, and standard color film, such as Ektachrome from Kodak. All of these are expensive and lack the resolution of black and white x-ray film that radiologists have become familiar with and have come to depend upon. Neither of the hard copy media (color print film and color thermal prints) produce high quality diagnostic images from which the radiologist can discern subtle features of tissue structure important in diagnosing the pathology of the patient. For this reason, the color doppler feature of an ultrasound machine can be turned off to permit the recording of the grey scale image on more familiar x-ray film (black and white transparency). The x-ray film produces an image of very high quality, with high spatial resolution, wide dynamic range, and high contrast resolution. The cost of the x-ray film is also very low when compared to the color film; six images for about $1.00, whereas color film (either Polaroid or thermal print) costs about $6.00 for six images.
Standard color film presents several additional problems and, thus, has not been adopted by hospitals. In addition to the high cost of the film, it requires special processing, the film is subject to the color balance of the film shifting, and the processing time is long. The length of time to process the film alone would be a problem since the patient must be kept at the facility until the radiologist has had at least a chance to make an initial review of the images to determine whether the film was properly exposed and developed, etc.
As a result of the short comings of the presently available media for making hard copies of such color enhanced images there has developed a need for a fast, inexpensive, media that produces a high quality color image (high spatial resolution, wide dynamic range, high contrast resolution and stable color balance), and the method for producing and viewing such a storage media. The present invention meets all of these criteria.